Switching regulators are used to provide a constant supply of voltage to the circuitry within prescribed voltage tolerances. They are often used in portable electronic devices that have lower power requirements where the input voltage is supplied by a power source, such as a battery, that may fluctuate overtime due to contact corrosion, dissipation, temperature or other external environment conditions or changes thereof. The switching regulator receives the input voltage from the power source and converts it to a voltage within the prescribed voltage tolerance. Thereby, the switching regulator provides a regulated output voltage to a load from an unregulated input voltage. Specifically, the switching regulator provides and maintains a predetermined output voltage to a portable electronic device circuitry coupled thereto. As such, circuitry incorporated within the switching regulator regulates the voltage to within prescribed voltage tolerances of the device circuitry even in the presence of wide deviations in the power source voltage.
The switching regulator may be used to convert a power source signal to a higher or lower controlled voltage output. A control circuit for generating pulse width modulation within the switching regulator functions as an oscillator which provides a periodic carrier signal. By rapidly opening and closing a switch within the switching regulator, the control circuit controls the average power that is provided to a load coupled to the switching regulator by controlling the average voltage applied to the load.
A typical switching regulator has at least two switches that switch ON and OFF out of phase with each other to supply current to a load. Three types of switching regulators include: buck mode switching regulators, which regulate an output voltage that is lower than the input voltage; boost mode regulators, which regulate an output voltage that is higher than the input voltage; and buck-boost mode switching regulators, which regulate an output voltage that is higher, lower, or the same as the input voltage. These three modes can be combined to form a multiple mode switching regulator.
A typical multiple mode switching regulator includes an inductor with a first end coupled to both a first high side switch, a first low side switch, and a second end coupled to both a second high side switch and a second low side switch. The first high side switch and first low side switch are on the input side. The second high side switch and second low side switch are on the output side. In buck mode, the first high side switch and first low side switch are switched ON and OFF out of phase with each other. In boost mode, the second high side switch and second low side switch are switched ON and OFF out of phase with each other. In buck-boost mode, the first high side switch and the second low side switch are switched ON and OFF in phase with each other, and the second high side switch and the first low side switch are switched ON and OFF in phase with each other, but out of phase with the first high side switch and second low side switch.
Advantageously, switching regulators are often used in electronic devices because of their greatly increased efficiency at higher loads. This increase in efficiency presents a substantial advantage for battery powered devices. The efficiency, however, is reduced greatly when a minimal current load is present. As a solution, a switching regulator may include a low power mode to increase the efficiency when the load current has fallen below a certain predetermined threshold. During the low power mode, various blocks within the regulator are turned off and a simpler control loop may be employed. Unfortunately, the simpler control loop decreases regulation tolerance.
Most switching regulators do not implement a low power mode that maintains a regulated output voltage. Many switching regulators that include a low power mode do not automatically sense the output current in an effort to make a determination of whether the low power mode should be entered or exited from. Furthermore, many of these switching regulators require a low power mode input signal to initiate the low power mode. There, however, are a few switching regulators that sense the output current and provide a feature of automatic entrance and exit from a low power mode. Unfortunately, these switching regulators require an expensive precision resistor or a current transformer to sense current and are dependent on the capacitor value and input and output voltage.
Thus, a need exists for a switching regulator having a low power mode that automatically senses when this mode should be initiated without the use of expensive external components nor an extensive amount of external components.